Details of Grant 

EPSRC Reference:	GR/J42090/01
Title:	ALL OPTICAL FABRICATION OF SEMICONDUCTOR DEVICES
Principal Investigator:	Marsh, Professor JH
Other Investigators:	De La Rue, Honorary Professor R Coleman, Professor A
Researcher Co-Investigators:
Project Partners:
Department:	Electronics and Electrical Engineering
Organisation:	University of Glasgow
Scheme:	Standard Research (Pre-FEC)
Starts:	01 September 1993	Ends:	31 August 1995	Value (£):	105,175
EPSRC Research Topic Classifications:	Optoelect. Devices & Circuits
EPSRC Industrial Sector Classifications:
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Summary on Grant Application Form
To develop a new technology for fabricating photonic integrated circuits primarily in the GaInAs/GaInAsP material system The technique is a laser-based quantum well intermixing process called photo absorption induced disordering (PAID) To establish the spatial resolution of PAID. To demonstrate the use of the process to form gratings in optoelectronic waveguide devices. To probe the nature of laser induced defects by using QW monitoring layers. To assess the nature and extent of any residual defects after an annealing cycle. Progress:Photo-absorption induced disordering (PAID) is a laser induced quantum well intermixing (QWI) technique particularly suited to the GaInAsP quaternary. GaInAsP is of limited thermal stability and QWI takes places at temperatures >520 C. In the first variation of the PAID technique, a cw beam from a Nd:YAG laser has been used to heat the semiconductor so that intermixing occurs without the melting point of the semiconductor being approached. Using this process it is possible to modify the bandgap in selected areas of a wafer after growth. A range of bandgap tuned devices, which includes all of the key components in practical PICs, has been fabricated and assessed. Broad area oxide stripe lasers have been fabricated from GaInAs/GaInAsP multi-quantum well laser material which has undergone various degrees of intermixing by PAID, and blue shifts of up to 160 nm in the lasing spectra have been demonstrated. The bandgap tuned lasers have also been assessed in terms of threshold current density, internal quantum efficiency and internal loss. The threshold current density shows a small increase as the degree of intermixing increases, commensurate with moving from a well-confined 2D structure to a more 3D like structure. The internal quantum efficiency essentially remains constant. The internal loss of the lasers decreases as the material is intermixed which is attributed to a reduction in Auger recombination as the wavelength of operation is shortened. The excellent device performance demonstrates that the residual defect concentration is low. Electroabsorbtion waveguide modulators have been fabricated in a similar MQW structure in which the bandgap was widened by up to 120 nm. ON/OFF ratios >20 dB were measured in 500 -m long devices for a voltage swing of only 3 V, while samples shifted by 80 nm gave modulation depths as high as 27 dB. Passive waveguides have also been made with losses around 5 dB/cm, measured at a wavelength corresponding to the lasing wavelength of as-grown material. The spatial resolution of the cw PAID process is around 100 -m, so a pulsed variation of the technique is being developed. Material is irradiated with pulses from a Q-switched Nd:YAG laser, typically of around 8 ns in duration, and is then annealed at 700C in an RTP for several minutes. The resolution of the disordering process has been investigated across a masked interface using PL, and has been determined to be <25 -m (limited by the resolution of the PL system). TEM is being used to determine the true resolution more sensitively. Devices are being fabricated using the pulsed PAID process. In conclusion, a versatile fabrication process is being established for 1.5 and 1.3 -m photonic integrated circuits.
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